Electrochemical cells convert fuel and oxidizing agents into electricity, heat, and water at two spatially separated electrodes, an anode and a cathode. The energy conversion process in electrochemical cells is distinguished from other energy conversion processes by its relatively high efficiency. For this reason, electrochemical cells are becoming increasingly important for transportation, mobile, stationary, portable, and micro applications.
During operation of an electrochemical cell, fuel reacts at an anode catalyst layer to form protons and electrons. The protons migrate through an ionomer exchange membrane to the cathode, while the electrons perform external work in a load before reaching the cathode. At the cathode, an oxygen-containing reactant (oxidant) supply combines with the protons and electrons to form water as a reaction product.